I love this Free People sweater.
Yes I know I love all things Free People! Lol
Go to thrift store. Purchase a sweater and a sweatshirt combo you like. :) they need to be similar sizes most importantly in the arm area.
Line up arms of sweatshirt and sweater cut accordingly. Trim up the side seam and trim the top wide enough.Pin. And pin. Bc the stretch sweater will stretch if you don't almost over pin.
Now sew!! I did it all at once but looking back probably easier to do body first then the arms. But I'm rouge! I sewed over every area 3x with the sweatshirt being the outer hem kinda raw seam.